What is the current leading hypothesis regarding the nature of dark matter, and what experimental or observational evidence supports this hypothesis?

Based on the observational evidence, is it possible that dark matter doesn't really exist?

A statement found to be experimentally valid over a wide range ofobserved phenomena is referred to as a

a. model.
b. principle.
c. theory.
d. hypothesis.
e. law.

The moon is observed to have phases in which only a portion of themoon appears to be illuminated. The cycle of phases repeats itselfapproximately every month. Compose a scientific hypothesis toexplain this observation of the moon. Then explain what tests ofyour hypothesis could be made.